Ethylene Oxide (EtO) Sterilization

This law states that the mass of a substance altered at an electrode during electrolysis is directly proportional to the quantity of electricity transferred. The relationship is expressed by the formula \(m = \frac{Q}{F} \frac{M}{z}\), where m is mass, Q is total electric charge, F is the Faraday constant, M is molar mass, and z is the valence number of ions of the substance.

A physical sterilization method that removes microorganisms from liquids and gases by passing them through a filter with a pore size small enough to retain the microbes. A common pore size for sterilizing filtration is 0.22 micrometers (µm), which effectively removes most bacteria. This technique does not kill microorganisms but physically separates them, making it ideal for heat-labile solutions.

The D-value is the time required at a specific temperature to kill 90% (or one log reduction) of a target microorganism population. It is a critical parameter in thermal sterilization, quantifying a microbe's resistance to heat. For example, if a population of \(10^6\) spores has a D-value of 2 minutes, it takes 2 minutes to reduce it to \(10^5\).

Cytotoxicity is the quality of a substance or cell being toxic to other cells. Cytotoxic agents can induce cell death through necrosis, where the cell membrane loses integrity leading to lysis and inflammation, or apoptosis, a controlled, programmed cell death process. This is distinct from cytostatic agents, which only inhibit cell division without directly causing cell death.

Natural Killer (NK) cells are cytotoxic lymphocytes of the innate immune system, critical for early defense against viral infections and cancer. Unlike T cells, they do not require prior sensitization. NK cells identify and kill target cells that have downregulated MHC class I molecules—a common immune evasion tactic by tumors and viruses—through a "missing-self" recognition mechanism, inducing apoptosis via perforin and granzymes.

Biomimicry is an innovation approach that seeks sustainable solutions to human challenges by emulating nature's time-tested patterns and strategies. The core idea is that nature, through 3.8 billion years of evolution, has already solved many of the problems we are grappling with. It involves observing and learning from the designs and processes of organisms and ecosystems to create more sustainable designs.

The electrolysis of water is the decomposition of water (H₂O) into its constituent elements, oxygen (O₂) and hydrogen (H₂), by passing an electric current through it. At the cathode, two water molecules are reduced to form hydrogen gas and hydroxide ions. At the anode, two water molecules are oxidized to form oxygen gas, protons, and electrons.

A method using high-pressure saturated steam at high temperatures to sterilize equipment and supplies. A typical cycle is 121 °C (250 °F) at 100 kPa (15 psi) above atmospheric pressure for 15 minutes. This combination of heat and moisture effectively denatures proteins and enzymes, killing all microorganisms, including resilient bacterial spores.

Overpotential is the potential difference (voltage) between a half-reaction's thermodynamically determined reduction potential and the potential at which the redox event is experimentally observed. It represents the extra energy required to overcome activation barriers for the electrode reaction to proceed at a significant rate. It is a key factor in the energy efficiency of all electrolytic processes.

Cellular respiration is a series of redox reactions where organic molecules, like glucose, are oxidized to release energy. Glucose (\(C_6H_{12}O_6\)) is oxidized to \(CO_2\), while oxygen (\(O_2\)) is reduced to water (\(H_2O\)). This process transfers electrons through an electron transport chain, creating a proton gradient that drives the synthesis of ATP, the cell's primary energy currency.

Electrochemical potential is fundamental to life, driving processes across cell membranes. Ion pumps actively create concentration gradients, while the selective permeability of ion channels establishes an electrical potential (membrane potential). The resulting electrochemical gradient dictates the passive flow of ions, which is crucial for nerve signaling (action potentials), muscle contraction, and cellular energy production (ATP synthesis) in mitochondria.

SAL is a quantitative measure representing the probability of a single viable microorganism surviving on an item after sterilization. A commonly required SAL for medical devices is \(10^{-6}\), meaning a one-in-a-million chance of a non-sterile unit. This probabilistic approach acknowledges that absolute sterility cannot be proven, only inferred statistically from process validation.

The MTT assay is a colorimetric method for assessing cell metabolic activity, which serves as a proxy for cell viability, proliferation, and cytotoxicity. Viable cells with active mitochondria contain reductase enzymes that convert the yellow tetrazolium salt MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) into an insoluble purple formazan. The amount of formazan produced is proportional to the number of living cells.